Field of the Invention
The field of the invention is internal combustion engines.
Engines have been developed that operate using a lean-burn system wherein the air component of the fuel-air mixture is increased by increasing the air intake flow into the cylinder. By increasing the air component of the fuel-air mixture, the efficiency and power of the engine are improved. Consequently, by increasing the quantity of air, not only is the power output increased, but the fuel consumption is reduced, thereby improving gas milage.
Typically, during an intake stroke of an internal combustion engine, a mixture of fuel and air is introduced into an engine cylinder After the intake stroke, the compression stroke commences, thereby compressing the mixture of fuel and air within the cylinder. A spark plug typically ignites the fuel-air mixture within the cylinder to provide power via the piston located within the cylinder. An exhaust stroke removes the burned fuel and air mixture from the engine cylinder in anticipation of the next intake stroke.
Generally, as the fuel-air mixture is compressed, the mixture of fuel and air near the spark plug electrode is richer, or thicker than the surrounding gases. When the electrode of the spark plug discharges, the region containing the thicker mixture of fuel and air is the first to ignite. The flame then travels outward, along the inner surface of the combustion chamber where the mixture is thinner, i.e., leaner. Finally, the flame spreads to the main area of the combustion chamber, where the mixture of fuel and air is leanest.
Unfortunately, this mixture of fuel and air in the main combustion chamber takes longer than desired to finish burning. This problem is particularly acute when a lean fuel mixture is used in the engine. This is so because the fuel particles in the lean fuel-air mixture are located at further distances from one another than in normal fuel mixture conditions. Consequently, in a typical engine using a lean fuel-air mixture, the thermal efficiency is lowered because of slow flame propagation and combustion within the cylinder.
Attempts have been made to prevent this situation from occurring by modifying the flow of the fuel-air mixture. To this end, various mechanisms have been developed that are incorporated into the intake system to add a strong swirl to the intake fuel-air mixture. Since the individual particles in lean-burn systems are separated from one another by large comparative distances, it is preferable to force the particles toward one another by actively moving the particles. By adding a strong swirl in the cylinder to the fuel-air mixture, a homogenization of the fuel-air mixture is accomplished.
By adding a strong swirl to the combustion chamber, the distances between fuel particles decreases. The decreased particle distances and the increased particle motion caused by the strong swirl increases the flame propagation speed. In addition, filing efficiency is increased by adding a swirl to the cylinder.
Various designs have been attempted in combustion engine intake systems to increase turbulence within the cylinder. For example, automobile manufacturers have used two intake ports and two valves, where one valve is partially closed to generate a swirl within the cylinder. Unfortunately, these methods have had deleterious side effects on engine performance, such as strong intake resistance, pumping loss, and lower filling efficiency. Moreover, these methods are able to generate a strong swirl only under low-load conditions when used within a four-valve structure. Accordingly, there is a need for a multi-valve intake and exhaust system that increases flame propagation speeds, improves intake and exhaust efficiency, and permits the formation of swirls within the cylinder over the entire revolution range without swirl interference.